Field of the Invention
The present invention relates to an image printing apparatus and an image printing method.
Description of the Related Art
Image printing apparatuses that form an image on a printing medium by scanning a print head having a plurality of ink ejection ports arranged therein over the printing medium and, at the same time, ejecting ink from the ejection ports have been developed. Such image printing apparatuses employ a so-called multipass method in which a unit area of the printing medium is scanned a plurality of times. In recent years, to reduce the print time, reduction in the number of scans during printing has been required.
In such printing apparatuses, the ink droplet impacting position may be misaligned due to misalignment of a printing medium occurring during conveyance of the printing medium or the offset of the ink droplet ejecting direction occurring in an end portion of the ejection port array caused by an air flow generated by ink ejection. Thus, a stripe-shaped density unevenness (hereinafter referred to as “bond stripes”) may be formed in an image area formed by ink ejection from the ejection port in the end portion of the ejection port array. The bond stripes are more prominently formed as the number of scans for a unit area is smaller and as the ejection volume of ink in one scan is larger.
U.S. Patent Application Publication No. 2008/0252686 describes a printing method in which an image is formed in a first area of a printing medium by scanning a print head over the first area K times while an image is formed in a second area that differs from the first area of the printing medium by scanning the print head over the second area (K+1) times. In the printing method, the conveyance of a printing medium is controlled so that in each of two of (K+1) scans over the second area, a plurality of ejection ports arranged in each of both end portions of the ejection port array correspond to the second area. According to U.S. Patent Application Publication No. 2008/0252686, by performing control so that the ejection volume per scan during (K+1) scans over the second area is less than the ejection volume per scan during K scans over the first area, high-speed printing is available without the occurrence of the above-described bond stripes.
However, in the technology described in U.S. Patent Application Publication No. 2008/0252686, uneven gloss may be generated between an image printed in the first area and an image printed in the second area and, thus, the quality of the entire image may decrease.
Such an issue is described in more detail below.
Note that in the following example, an image is formed in two scans over the first area and three scans over the second area.
If printing is performed using the printing method described in U.S. Patent Application Publication No. 2008/0252686, an image is printed in three scans over the entire second area. Accordingly, the formed image includes an image printed in the first area in two scans and an image printed in the second area in three scans.
Note that in general, the glossiness decreases with increasing number of scans in which ink is ejected onto an area of the printing medium. This is because if the number of scans in which ink is ejected onto the same area increases, an image is formed by stacking ink droplets one on top of another and, thus, the surface irregularities of the final image increase. As a result, the glossiness decreases.
Accordingly, in the printing method described in U.S. Patent Application Publication No. 2008/0252686, an image having a relatively high glossiness in the first area and an image having a relatively low glossiness in the second area are alternately formed along the conveyance direction of the printing medium. In this manner, images having different gloss levels are present on the printing medium, and the human eye instantly recognizes the uneven gloss.
If an image is printed in three scans over the entire area of the printing medium, the period of time until completion of printing is completed relatively increases.